Power supply device with low power dissipation

Abstract

An improved power supply device decreases the amount of power used in computer and computer peripheral devices by utilizing a control transistor which is set into a switching operation responsive to a pulse signal received from a power supply control circuit. The control transistor controls the voltage applied to the primary winding of the power transformer by a switch transistor, and issues an output voltage from the secondary winding. The power supply device includes a switch circuit which is connected in series to a starting resistor for supplying the output voltage rectified from the AC power source when starting up to the power supply control circuit. The power supply device includes a switch-control circuit which turns off the switch circuit when the output voltage rectified from the AC output of the tertiary winding of the power transformer reaches a voltage high enough for stable operation of the power supply control circuit. The present invention is characterized by a separation device, coupled to the starting terminal of the power supply control circuit and the power source of the tertiary winding of the power transformer, to ensure that there is no need for an extremely high voltage to drive the switch-control circuit. As a result, the power loss at the starting resistor is eliminated after startup of the power supply device such that the power consumption of the power saving operation is also eliminated.

What is claimed is: 
     
       1. A power supply device with low power dissipation, comprising: a DC voltage;   a control transistor, receiving a switching signal and performing turn-on/turn-off operations;   a power transformer, including at least a primary winding, a secondary winding, and a tertiary winding, for producing an output voltage in said secondary winding and said tertiary winding, respectively, when said DC voltage is applied to said primary winding controlled by said control transistor;   a power supply control circuit, activated when a voltage of a starting terminal of said power supply control circuit reaches a starting voltage level for outputting said switching signal to said control transistor;   a path for said DC voltage to charge a starting capacitor and provide said starting voltage to said starting terminal through a starting resistor, in order to activate said power supply control circuit;   a switch circuit, connected in series to said starting resistor and said power supply control circuit;   a switch-control circuit, including an input terminal coupled to said output voltage of tertiary winding controlling the turn-on/turn-off operations of said switch circuit, wherein said switch-control circuit turns off said switch circuit to prevent additional power consumption by said starting resistor when said output voltage of tertiary winding reaches a specific threshold voltage; and   a separation device, coupled between said starting terminal of said power supply control circuit and said input terminal of said switch-control circuit, to ensure that said switch-control circuit will not be activated to turn off said switch circuit by said starting voltage which is higher than said specific threshold voltage of tertiary winding.   
     
     
       2. The power supply device of claim 1, wherein said separation device is a diode having an anode coupled to said switch-control circuit and an output terminal of said tertiary winding of said power transformer, and a cathode coupled to said starting terminal of said power supply control circuit. 
     
     
       3. The power supply device of claim 1, wherein said switch circuit includes a first transistor having a collector coupled to a terminal of said starting resistor, an emitter coupled to said starting terminal of said power supply control circuit, and a base coupled to said switch-control circuit and said switch-control circuit includes a second transistor having a collector coupled to said base of said first transistor and coupled to said DC voltage source via a biased diode, an emitter coupled to a reference ground terminal of said power supply control circuit, and a base coupled to an output voltage source of said tertiary winding of said power transformer providing a base current to said base of said second transistor. 
     
     
       4. The power supply device of claim 3, wherein IC 3842 series or 3844 series can serve as said power supply control circuit. 
     
     
       5. The power supply device of claim 4, further including a protective; forward-biased diode between said emitter of said first transistor and said starting capacitor. 
     
     
       6. The power supply device of claim 4, wherein said separation device is a diode having an anode coupled to said switch-control circuit and said output voltage source of said tertiary winding of said power transformer, and a cathode coupled to said starting terminal of said power supply control circuit. 
     
     
       7. The power supply device of claim 6, further including a protective; forward-biased diode between said emitter of said first transistor and said starting capacitor. 
     
     
       8. The power supply device of claim 3, wherein said separation device is a diode having an anode coupled to said switch-control circuit and said output voltage source of said tertiary winding of said power transformer, and a cathode coupled to said starting terminal of said power supply control circuit. 
     
     
       9. The power supply device of claim 8, further including a protective; forward-biased diode between said emitter of said first transistor and said starting capacitor. 
     
     
       10. The power supply device of claim 3, further including a protective; forward-biased diode between said emitter of said first transistor and said starting capacitor. 
     
     
       11. The power supply device of claim 1, wherein IC 3842 series or 3844 series can serve as said power supply control circuit. 
     
     
       12. The power supply device of claim 11, wherein said separation device is a diode having an anode coupled to said switch-control circuit and said output voltage source of said tertiary winding of said power transformer, and a cathode coupled to said starting terminal of said power supply control circuit.